The lecture abstract:Alien chromosomes from related species have been transferred to bread wheat during the production of chromosome addition and alloplasmic lines. Some of these chromosomes behave as selfish genetic elements that are preferentially transmitted to the offspring, and were designated as gametocidal chromosomes and the genes causing these effects as Gc genes. Previous studies revealed that Gc genes ensure their preferential transmission by causing chromosome breakage in male and female gametophytes lacking them. We are working with the Gc2 gene, which was named 'cuckoo' because of its selfish behavior by Terry Miller, and was transferred to wheat from Aegilops sharonensis in the form of a wheat-Ae. sharonensis translocation chromosome T4BS.4BL-4Ssh#1L. Gc2 causes extensive chromosome fragmentation in gametophytes lacking the Gc2 gene, which are nonfunctional and, as a result all progenies derived from Gc2/+ hemizygotes are homozygous Gc2/Gc2. We have identified three EMS-induced knock out mutations that indicated that the Gc2 gene is composed of two components, one causing chromosome breakage in gametophytes lacking it and another component that protects Gc2 gametophytes from chromosome fragmentation. The EMS-induced mutations are knockouts of the 'breaking' component. We have developed mapping populations and have identified molecular markers that flank the Gc2 locus. I will discuss the status of the map-based cloning of the Gc2 gene and will also address some practical applications for wheat improvement.